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Molecular and Cellular Biology, August 2008, p. 4782-4793, Vol. 28, No. 15
0270-7306/08/$08.00+0     doi:10.1128/MCB.00330-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Phosphorylation of the Budding Yeast 9-1-1 Complex Is Required for Dpb11 Function in the Full Activation of the UV-Induced DNA Damage Checkpoint ^,

Fabio Puddu, Magda Granata, Lisa Di Nola, Alessia Balestrini,^¶ Gabriele Piergiovanni, Federico Lazzaro, Michele Giannattasio, Paolo Plevani,^* and Marco Muzi-Falconi^*

Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milan, Italy

Received 27 February 2008/ Returned for modification 26 March 2008/ Accepted 27 May 2008

Following genotoxic insults, eukaryotic cells trigger a signal transduction cascade known as the DNA damage checkpoint response, which involves the loading onto DNA of an apical kinase and several downstream factors. Chromatin modifications play an important role in recruiting checkpoint proteins. In budding yeast, methylated H3-K79 is bound by the checkpoint factor Rad9. Loss of Dot1 prevents H3-K79 methylation, leading to a checkpoint defect in the G₁ phase of the cell cycle and to a reduction of checkpoint activation in mitosis, suggesting that another pathway contributes to Rad9 recruitment in M phase. We found that the replication factor Dpb11 is the keystone of this second pathway. dot1 dpb11-1 mutant cells are sensitive to UV or Zeocin treatment and cannot activate Rad53 if irradiated in M phase. Our data suggest that Dpb11 is held in proximity to damaged DNA through an interaction with the phosphorylated 9-1-1 complex, leading to Mec1-dependent phosphorylation of Rad9. Dpb11 is also phosphorylated after DNA damage, and this modification is lost in a nonphosphorylatable ddc1-T602A mutant. Finally, we show that, in vivo, Dpb11 cooperates with Dot1 in promoting Rad9 phosphorylation but also contributes to the full activation of Mec1 kinase.

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* Corresponding author. Mailing address: Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milan, Italy. Phone for Marco Muzi-Falconi: 39 02 50315034. Fax: 39 02 50315044. E-mail: marco.muzifalconi{at}unimi.it. Phone for Paolo Plevani: 39 02 50315032. Fax: 39 02 50315044. E-mail: paolo.plevani{at}unimi.it

Published ahead of print on 9 June 2008.

Supplemental material for this article may be found at http://mcb.asm.org/.

These authors contributed equally to this work.

Present address: Teva Pharma Italia, Milan, Italy.

^¶ Present address: Genome Stability Unit, Clare Hall Laboratories, London Research Institute, London, United Kingdom.

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Molecular and Cellular Biology, August 2008, p. 4782-4793, Vol. 28, No. 15
0270-7306/08/$08.00+0     doi:10.1128/MCB.00330-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Navadgi-Patil, V. M., Burgers, P. M. (2008). Yeast DNA Replication Protein Dpb11 Activates the Mec1/ATR Checkpoint Kinase. J. Biol. Chem. 283: 35853-35859 [Abstract] [Full Text]  
• Mordes, D. A., Nam, E. A., Cortez, D. (2008). Dpb11 activates the Mec1-Ddc2 complex. Proc. Natl. Acad. Sci. USA 105: 18730-18734 [Abstract] [Full Text]